Planet Earth
 
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The origin of the Earth

Earth from Space

Our solar system and its planets formed approximately 4.5 billion years ago when thousands of asteroids were pulled together by gravity. A large volume of gas and dust formed in the centre as the sun.

Earth (together with other planets) was initially a galactic punching bag for millions of crashing asteroids. Radioactivity heated the Earth from within and allowed heavier elements to concentrate at its core.

The Earth in the Solar System

The solar system is made up of the Sun, nine planets and their 137 known moons as well as asteroids, comets, dust and gas. The Earth is situated approximately 150 million kilometers from the Sun. The planets, asteroids and comets travel around the Sun, which is a massive star at the centre of our solar system. Most of the bodies in the solar system travel around the Sun along nearly circular paths or orbits, in an anticlockwise direction.

 

The structure of the Earth
The Earth's Crust

A Scotch Egg
Imagine a Scotch egg......

        1. The outer shell of the Earth is called the CRUST (breadcrumbs)
        2. The next layer is called the MANTLE (sausagemeat)
        3. The next layer is the liquid OUTER CORE (egg white)
        4. The middle bit is called the solid INNER CORE (egg yolk)

The Earth is a sphere-like shape (like the scotch egg!) with a diameter of about 12,700 kilometres. As we go deeper and deeper into the earth the temperature and pressure rises.

The crust is on average 20 km thick. If the Earth was the size of a football, the crust would only be about ½ millimetre thick. The thinnest parts are under the oceans (Oceanic Crust) and go to a depth of roughly 10 kilometres. The thickest parts are the continents (Continental Crust) which extend down to 35 kilometres on average. The continental crust in the Himalayas is 75 kilometres deep.

The mantle is the layer beneath the crust which extends about half way to the centre. It's made of solid rock but can flow over very long periods of time. The convection of heat from the centre of the Earth is what ultimately drives the movement of the tectonic plates and cause mountains to rise. Click here for more details

The outer core is the layer beneath the mantle. It is made of liquid iron and nickel. Complex convection currents give rise to a dynamo effect which is responsible for the Earth's magnetic field.

The inner core is the bit in the middle! It is made of solid iron and nickel. Temperatures in the core are thought to be in the region of 5000-6000°c and it's solid due to the massive pressure. 



The age of the Earth
There are no written historical documents dating back to when the earth was formed, therefore scientists have had to use rocks, and the fossils preserved in them, to work out what happened on earth all those years ago. By studying the geology in the form of rocks and fossils scientists have been able to track the events that have occurred on our planet since it was first formed approximately 4,600 million years ago. The timescale that is used to show the changes in geology over time is called geological time. Click here to learn about the Age of the Earth.


Links
www.bbc.co.uk/science/space/